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| Design fin can | Approx. Time Required | # People Required | Notes |
|---|---|---|---|
| Fin Design & Manufacturing | 36 hours | The more the merrier. | Manufacturing procedure and detailed breakdown described in "Hermes 2 Fin Design & Manufacturing" |
| Design/make jigs | |||
| Root bond jig | 3 | 2 | Allow for tolerance so fins fit, but don't make slots too loose. Make sure you have a top plate. Second Set (correct fit):
First Set (collar too small)Too small:
|
| Fillet jig | used H2's | N/A | Two wooden pieces with a U-shaped slot on which the fin can rests horizontally. |
| Fillet tools | 2 | 1 | |
| Tube preparation | |||
| Tube layup | 6 | 2-4 | Rough up the outside of the tube before layup. |
| Root bond | 2 | Used 5 minute epoxy because this is a practice fin can. Noticed gaps between the fins and the collar. | |
| Root fillets | 6 | Did two fillets a day for a total of 8 fillets over 4 days. Degassed Systems 3000 epoxy in the vacuum chamber before applying epoxy to fin. Need to sand the fin better. | |
| Layup preparation | |||
| Laser-cut CF cutouts | 4 | 2 | Be careful not to laser-cut over the taped edges of the carbon fiber squares that you use for the cutouts (the tape will be difficult to remove and fray the fibers). Also, don't spray glue wax paper until after laser cutting because the wax paper might catch fire or start smoldering in the laser cutter. |
| Spray-glue to wax paper | 1 | 2 | |
| Sand fillets | 0 | If you do the fillets right, you should barely have to sand them. Make sure to wear a respirator whenever sanding fiberglass. | |
| Prep vacuum materials | 3 | 4 | The shape of each vacuum bagging material (peel ply, breather, bleeder, vacuum bag) should be a square, and you need four squares of each material since there are four fins. The width of the cutouts should be around 4 inches longer than the tip-to-tip distance (not too long or too short). The length of the cutouts should be around 4 inches longer than the fin collar (see images to get an idea of the size). The sizes for Rusty were not correct. Dusty will have the correct sizes listed. |
| Layup | |||
| Wet plies/weight | |||
| Layup | 8 | ||
| Put on vacuum bagging | 2 | ||
| Vacuuming | 24 | Watch the gauge on the vacuum pump to make sure it drops to at least -26 mm Hg | |
| Oven Cure | |||
| Set up oven/vacuum materials | |||
| Follow epoxy cure cycle | 12 hours | See oven shift google doc. | |
| Remove vacuum materials | This takes a while, but it can be done with patience. Make sure you don't lose track of any of the vacuuming supplies (like the vacuum pump attachment) when you throw out the bagging materials. | ||
| Clean up edges | We didn't clean up any edges because this was a practice fin can. | ||
| Static load test | This section has yet to happen because Shannon and Charlie are working on a fin can test jig. Will update later. | ||
| Design/build jig | |||
| Determine testing loads | |||
| Static load test | |||
| Analyze data | |||
| Post-processing | No post-processing was done for Rusty | ||
| Sand fillets/outside | |||
| Outer fillets on low spots | |||
| Paint | |||
| Total manufacturing time |
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- CF overwrapped tube
- Systems 3000 epoxy (resin and hardener)
- Acrylic fillet radius tool
- Gloves
- Respirator
- Carbosil
- Popsicle sticks
- Epoxy boats or paper cup (for mixing epoxy)
- Painters tape
- Ruler
- Acetone and shop towels (to clean up epoxy on acrylic tools)
- Vacuum
- Root bond jig
- Sandpaper (220 grit)
Root Bond Procedure
- Measure the outer diameter of the overwrapped fin can. Use this measurement to
Used System 3000 epoxy. fin can jig needs to be improved --> make sure to space layers evenly, use top layer with smaller slits. Holes were slightly too small so was difficult to adjust
AFTER root bond, attached phenolic LE to G10 fin core (did after root bond because phenolic wouldn't have fit in the fin can jig)
Root fillet (West Systems fast hardener + colloidal silica)
Says it takes 6 hours to cure, but if you're in a time crunch you can apply a new fillet every 3-4 hours. Can use a heat gun to speed this up even more.
Sand fillets
Make sure to do fillets right the first time because this time we had to fill them in again (using West systems + fast hardener + silica)
talk about scheduling!! also speed up to tacking w/ heat gun
Procedure:
3.0 Progression of the Carbon Fiber Cut-outs Design
Last year, the tip-to-tip design called for 6 layers of 3 distinct sizes, 2 plies per size. This allowed for a tapering effect on the surface of the fins and the tabs at the top added extra layers above the fins (WHY?)
This first design had much room for improvement, however. The upper tabs going in both directions made aligning the layers more difficult during the layup. To fix this, the upper tabs only extend in one direction such that they are double the width of the fin-to-fin distance. In addition, the fin can extends below the fins themselves so a bottom tab was added to each layer. Another issue was that the taper between layers was too quick, creating actual bumps at each ridge where the layers size changed. To fix this, the design was changed to 6 distinct layers, 1 ply per size, which were offsets of the largest size which covered the entire tip-to-tip surface such that the leading edge and tip edge for each layer are half an inch apart and the trailing edge is a quarter of an inch apart. The final addition was an inch long offset on the largest layer on the tip edge and the trailing edge, the sections which will not have phenolic, to make sure that the fins are completely covered when the last layer is added. These considerations led to the fin design below:
This design was used for the first fin can flight candidate. The layup for this fin can revealed other issues with this design. Firstly, the ridge between the phenolic edge and fins was unfavorable so in the new design, there was no tapering from the leading edge of the fin. In addition, there were some gaps in the carbon fiber between the lower tabs so a half inch tab was added to the lower tab of each layer (tabception). This was to ensure that each layer would meet in that section of the fin. Another issue seen in the layup is that there were sections in the layup with only one layer of coverage, a possible site for improper heat maintenance. To fix this, the second to last layer of the layup is the same shape as the last, only lacking the extra offset on the tip and trailing edge. These changes resulted in the design below:
- to size the diameter of the hole for 4 root bond jig plates.
- Measure the thicknesses of the fins. Use this measurement to size the slots for 3 of the 4 plates. The bottom one should not have slots in order for the fins to rest on it.
- Use the threaded rods to evenly stack the plates on the root bond jig, and use a level to make sure that each plate is aligned properly.
- Apply Systems 3000 epoxy on the root chord of the fin preform (Without the leading edge attached), and slide the fin preform into the slot of the root bond jig to attach.
- Tape popsicle sticks each slot where the fin ends so that the fin can be held in place.
- Leave to room temperature cure for 24-36 hours before attaching leading edge and starting fillets.
| Part | Size |
|---|---|
| Diameter of collar | 6.27" |
| Width of slot | .131" |
| Length of slot | |
| Diameter of rod |
Root Fillet Procedure
- While wearing a respirator, mix 100 parts Systems 3000 resin with 18 parts hardener.
- Add in carbosil in small amounts and mix until a peanut butter consistency is achieved.
- Place the epoxy cup in the vacuum chamber, and wait 2 minutes. The epoxy should rise and then fall after the air bubbles have been pulled out.
- Mark the radius of the fillet on the fin and on the fin collar with a sharpie, and then cover in tape. In this case, Rusty had a one-inch fillet.
- Apply the epoxy in the fillet area, being careful not to go outside the tape.
- Use the acrylic fillet radius tool to remove excess epoxy. Be sure to swipe perpendicular to the root to ensure that the same amount of epoxy is being removed each time.
- Let it cure at room temperature for 24-36 hours.
- Place in the oven in the vertical position to oven cure for 12 hours.
- Sand the fillets.
3.0 Progression of the Carbon Fiber Cut-outs Design
Last year, the tip-to-tip design called for 6 layers of 6 distinct sizes. This allowed for a tapering effect on the surface of the fins and the tabs at the top added extra layers above the fins.Further analysis of the design gave three more changes before creating the next fin can. The first was a simple change; the upper tab was made slightly larger, 10.0" instead of 9.8", to make sure that each layer reached the next tab over. Next was the issue of carbon fiber not reaching the phenolic leading edge so as a precaution, the leading edge was offset by a quarter inch on each side. Though this would cause some excess carbon fiber to lie over the phenolic and this excess would need to be cut for each cutout, the extra time in doing so would allow us to cut to exactly the leading edge with the carbon fiber. The last change before the next lay up was the removing the taper on tip edge, mostly because we saw no need for it and only needed to see a smooth taper on the trailing edge, these changes resulted in the design below, the design used in the Hermes 2 Flight Candidate Fin Can #2:
3.1 Carbon Fiber Cut-outs for Tip-to-tip Layup
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